Controls on modern fan morphology in Calabria, Southern Italy

Alluvial fans are widespread throughout Calabria, but only a minority display evidence of current activity. In order to understand if and to what extent fan types and their morphology are dependent on the physical environment, including characteristics and processes of the depositional site and drainage basin, we performed a series of discriminant analyses. These analyses used as classification factors the presence or absence of fill in the feeder channel, conditions of confinement by host terrain, the dominant depositional process (debris-flow or sheetflood); and morphometric attributes of fans and drainage basins as the discriminant function variables. in general, fan slope, area and width-length ratio, and, for basins, Melton's ruggedness number and source ratio, were the most useful variables for classification. Best results were obtained by discriminating the types of fan deposits and the presence versus absence of fill in the feeder channel, if the feeder source is singular. Fan morphology is controlled by constructional processes and is tightly linked to basin morphology. On the other hand, fan and basin morphology are also strongly dependent on the rock mechanical characteristics, with hard rocks imparting to the basin a high ruggedness and to fans a high gradient. Larger fans, however, are those where sheetflooding predominates. Results of discriminant analysis based on fan and basin variables are much more significant than those based on fan variables only. This means that the differences between characteristics of fan-and-basin systems are better defined than those between characteristics of fans only. (C) 1998 Elsevier Science B.V. All rights reserved.